Process for improved water flux through a TFC membrane

Abstract

Provided is a process for preparation of a highly permeable thin film composite membranes for nanofiltration, reverse osmosis, and forward osmosis, particularly for reverse osmosis of brackish water. The process includes treating a prepared TFC membrane containing a discrimination layer on a frontside, a support layer, and a felt layer on the backside by contacting the backside of TFC membrane with a solution containing a pore protection agent that includes a tertiary amine salt of camphorsulfonic acid prior to or at the same time as contacting the frontside of the membrane with a solution containing a coating agent and drying the membrane. Also provided are reverse osmosis membranes prepared in accord with the method, and modules containing the highly permeable thin film composite membranes.

Description

FIELD OF THE INVENTION[0001]The present invention relates to thin film composite (TFC) membranes, including membranes used for nanofiltration, reverse or forward osmosis, e.g., to purify water, including tap water, brackish water (BW) and sea water (SW), and more particularly to additives and processes for enhancing water flux in TFC membranes.BACKGROUND OF THE INVENTION[0002]TFC membranes are membranes that have layers of dissimilar materials joined together to form a single membrane. This layered construction permits the use of material combinations that optimize performance and durability of the membrane. TFC membranes are used for nanofiltration, and in reverse osmosis and forward osmosis membranes for treating tap water, brackish water and sea water. Such membranes typically are made by interfacial polymerization of a monomer in a nonpolar (e.g., organic) phase together with a monomer in a polar (e.g., aqueous) phase forming a discrimination layer on a porous support layer. TFC...

AI Technical Summary

Benefits of technology

[0010]When the pore structure protection agent is included in a backside treatment solution and applied to the backside of a TFC membrane post-rinsing after interfacial polymerization and prior to drying or application of a frontside coating, the TFC membrane exhibits better water flux performance and maintains salt rejection after the drying process has been completed, compared to membranes prepared without application of a pore structure protection agent. With sea water TFC membranes, moderate water flux improvements can be realized using a pore structure protection agent in a backside treatment solution prior to drying or coating the membrane. With brackish water TFC membranes, large membrane flux improvements can be realized using a pore structure protection agent in a backside treatment solution. The lower pressures driving permeation under brackish conditions are believed to be the cause of the significant flux improvement for brackish membrane compared to sea water membranes. Under brackish conditions, restrictions to flow caused by pore collapse have a more significant effect because there is less driving force to overcome the restrictions caused by pore collapse.

[0011]It also has been determined that using a tertiary amine salt of camphorsulfonic acid as a pore protection agent has the added benefit of eliminating the possibility of osmotic blister formation that sometimes can occur when a drying agent such as sodium citrate is used. These osmotic blisters would manifest when the surface of the membrane was wetted and water sought to dilute the osmotic pressure difference caused by the sodium citrate salt concentration on the backside of the thin film. Since sodium citrate formed crystals when dried, the crystal could temporarily block the support pore layers, allowing osmotic pressure to build behind the thin film membrane. Any areas of the thin film membrane with weak adhesion to the support layer would delaminate, creating a blistered membrane that was susceptible to breakage by abrasion or any defects introduced in the membrane during its formation or handling. Using a tertiary amine salt of camphorsulfonic acid as the pore structure protection agent avoids any osmotic blister formation.

Problems solved by technology

Any areas of the thin film membrane with weak adhesion to the support layer would delaminate, creating a blistered membrane that was susceptible to breakage by abrasion or any defects introduced in the membrane during its formation or handling.

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